Growth of the dolphinfish Coryphaena hippurus from north-eastern Brazil with an appraisal of the efficacy of scales and otoliths for ageing

Age and growth of the dolphinfish Coryphaena hippurus caught off north-eastern Brazil were studied by counting growth increments on scales and otoliths. A sample (n = 2338) measuring 7·7-195 cm fork length (LF ) was collected from September 2001 to February 2003. The scales (n = 69) removed from six different regions of the body were examined and those from the caudal region exhibited greater morphological regularity, symmetry and a smaller rate of regeneration. The regression between caudal scale radius (RS ) and LF displayed was linear (LF = 28·334 RS + 9·186; r(2) = 0·754). Otolith micro-increments were counted assuming daily periodicity. Ages estimated from otoliths ranged from 64 to 659 days. The von Bertalanffy growth model was fitted based on the otolith readings generating L∞ = 194·1 cm LF , k = 0·912 year(-1) and t0 = 0·081 years. Species longevity was estimated to be c. 4 years. Ninety-eight per cent of the overall sample was adult specimens well above the age of first maturity in the study area. The large variability between scale length and LF and the failure to ascertain increment deposition periodicity suggest that scales are not appropriate for ageing C. hippurus and analysis of otolith micro-increments is deemed the best structure for ageing this species in the study area.